I was aware of the issue but, I forgot about it until I was past that point. I did have to remove completely the front and rear baffle brace in order to get the plenum to fit. But, after a few e-mails back and forth with Jan at RV Bits he said the plenum itself will take the place of that. So, I'm hoping it will also help with cracking issue in that corner.

Do give us a report on that at 500 hours.

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I did have a tech visit from Vic Syracuse and he wasn't too impressed with plenums overall.... he said most he has seen caused heating issues.....

I'm sure he meant to say a certain leading brand of plenum and cowl caused heating issues, a function of the inlets leading into the plenum, not the plenum itself.

In truth the plenum is the enclosed space about the engine. A stock Vans cowl installation with flap seals has a plenum, which functions the same as a plenum space with a separate lid, as we see here. That lid is unquestionably a better sealing device, as compared to flap seals.

Looks like your installation uses a standard RV-8 cowl. Measured pressure recovery for the stock cowl is quite good. Here the $100,000 dollar question is how you will seal those well-designed stock cowl inlets to your enclosed plenum space. Done poorly, that fancy plenum lid is just bling.

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I'm setting this plane up for acro and most of my friends say the plenum will keep the cowling from blowing up during the dives...... ????? ......

That is true. A decent set of inlets with tight plenum sealing and tight cylinder baffles will convert 80% or more of the available dynamic pressure to increased static pressure inside the plenum space. At 200 KTAS and 5000 feet on a standard day, that pressure would be 117 lbs per square foot x 0.8, or about 94 lbs. If we assume the lid to be 18" x 30" for a total of 3.75 sq ft, the total force trying to blow the plenum lid off the engine is 352 lbs. Doesn't matter if the plenum lid is a fancy carbon fiber thing tied to the baffle tin, or the upper cowl half.

The load is increased at lower altitude and higher airspeed. If designing sensibly, we probably want to ensure it will handle at least 230 KTAS at 2000 feet, just in case Bubba pulls a split-S from a roll or something. That would be 570 lbs at 0.9 efficiency.

I'm sure he meant to say a certain leading brand of plenum and cowl caused heating issues, a function of the inlets leading into the plenum, not the plenum itself.

In truth the plenum is the enclosed space about the engine. A stock Vans cowl installation with flap seals has a plenum, which functions the same as a plenum space with a separate lid, as we see here. That lid is unquestionably a better sealing device, as compared to flap seals.

Looks like your installation uses a standard RV-8 cowl. Measured pressure recovery for the stock cowl is quite good. Here the $100,000 dollar question is how you will seal those well-designed stock cowl inlets to your enclosed plenum space. Done poorly, that fancy plenum lid is just bling.

That is true. A decent set of inlets with tight plenum sealing and tight cylinder baffles will convert 80% or more of the available dynamic pressure to increased static pressure inside the plenum space. At 200 KTAS and 5000 feet on a standard day, that pressure would be 117 lbs per square foot x 0.8, or about 94 lbs. If we assume the lid to be 18" x 30" for a total of 3.75 sq ft, the total force trying to blow the plenum lid off the engine is 352 lbs. Doesn't matter if the plenum lid is a fancy carbon fiber thing tied to the baffle tin, or the upper cowl half.

The load is increased at lower altitude and higher airspeed. If designing sensibly, we probably want to ensure it will handle at least 230 KTAS at 2000 feet, just in case Bubba pulls a split-S from a roll or something. That would be 570 lbs at 0.9 efficiency.

Kinda puts cowls and plenum lids in a different light, eh?

DanH,

You are my hero! You've taught me how to fiberglass, cut and buff, the finer tuning of plenum design and a whole bunch of other stuff that I still don't understand! .... I even quoted you during a conversation with Jan at RV bits..... My plan is to use some gap seal from McMaster Carr along the top edges of the baffle slop to the cowl ramp and along the front edge of plenum at the inlet to provide a positive seal between the two. .... I have several different shapes and sizes to see what, (if any) works best. The only problem I see so far is the top seal may create a small bump in the air flow (but, it wont be a leak).... So far I've spent way to much time shaping, fitting and head scratching between the baffles, the "lid", the top cowl and the inlet ramps.... I finally just quit and figured I'd get back to that later..... I haven't gone as far as some to build a composite boot and I hope I don't have to.... If I understand Jan, they just slope the baffle ramps to the bottom of the cowl inlet ramps and glass up the ends.... we'll see for sure here soon....

Thanks for all you do for us "mere mortals" on the forum!!!!!
Any and all advice appreciated!

My plan is to use some gap seal from McMaster Carr along the top edges of the baffle slop to the cowl ramp and along the front edge of plenum at the inlet to provide a positive seal between the two. .... I have several different shapes and sizes to see what, (if any) works best.

Remember, the engine moves around quite a lot, notably nodding up and down in response to G, and rotating on the mounts in response to crankshaft torque. The seal must bridge the gaps throughout the range of motion. Without positive sealing, there is no reason to install a plenum lid.

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So far I've spent way to much time shaping, fitting and head scratching between the baffles, the "lid", the top cowl and the inlet ramps.... I finally just quit and figured I'd get back to that later.....

It will absolutely, positively, unquestionably be more of a PITA later. Figure out a sure plan and do whatever it takes, now, at home, in your shop.

I just used the hot temperatures the last weeks in Europe to start cutting the canopy to shape… Quite a frightening work.. But slowly it gets it shape

As I delayed riveting of my fwd top fuselage skin I thought I soon need to rivet it to be able to finish the windscreen. But I wanted to be finished with wiring.
And as visited some airshows this summer and also Luca Perrazoli in Italy, it was clear that I need a Smoke system. So the last days I ripped out my "finished and working" panel and added the cables for the smoke system.

Now I have a switch which "arms" the smoke system and I use the tiny small button on the Tosten Grips to switch the smoke on and off. The status "armed" and "on" are now shown on the G3X.

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